Why is bno passport a one-way ticket?

BNO passport is a one-way ticket because: BNO holders are allowed to visit the UK without a visa, but the stay is within six months, they do not have the right of residence and cannot work in the UK, and they do not enjoy any public benefits. ***Benefits, and can only be used once, have the same meaning as one-way tickets for high-speed rail and airplanes. The bno passport is a passport issued by the British government to Hong Kong people before Hong Kong returned to China in 1997.